1. Field of the Invention
This invention relates to a confocal scanning type of microscope. This invention particularly relates to a confocal scanning type of interference microscope for forming a visible image representing the phase information of a transparent sample.
2. Description of the Prior Art
Optical type scanning microscopes have heretofore been used. With the scanning microscope, a light beam is converged to a small light spot on a sample, and the sample is two-dimensionally scanned with the light spot. The light beam, which has passed through the sample during the scanning, the light beam, which has been reflected from the sample during the scanning, or the fluorescence, which is produced by the sample during the scanning, is detected by a photodetector. An enlarged image of the sample is thereby obtained.
As one type of the scanning microscopes, a confocal scanning microscope has heretofore been proposed. With the confocal scanning microscope, a light beam is produced by a light source and is condensed to a light spot such that an image of the light spot is formed on a sample. Also, a point image of the light beam, which has been radiated out of the sample, is formed and detected by a photodetector. The confocal scanning microscope is advantageous in that no pinhole plate need be located on the surface of the sample.
Basically, the confocal scanning microscope comprises:
i) a light source which produces a light beam,
ii) a sample supporting member on which a sample is supported,
iii) a light projecting optical means with which an image of the light beam is formed as a small light spot on the sample,
iv) a light receiving optical means with which the light beam radiated out of the sample (i.e. the light beam, which has passed through the sample, the light beam, which has been reflected from the sample, or the fluorescence produced by the sample) is condensed, and an image of the condensed light beam is formed as a point image,
v) a photodetector which detects the point image, and
vi) scanning mechanism for two-dimensionally scanning the sample with the light spot. An example of the confocal scanning microscope is disclosed in Japanese Unexamined Patent Publication No. 62(1987)-217218.
Also, an interference microscope has heretofore been proposed, with which the phase information of a transparent object (i.e. a phase object) can be investigated. Basically, with the interference microscope, before a light beam to be irradiated to a sample, which serves as a phase object, impinges upon the sample, the light beam is split into two light beams. Thereafter, the light beam, which has passed through the sample, and the light beam (i.e. the reference light beam), which has not passed through the sample, are combined with each other. An interference image is formed from the optical path difference between the light beam, which has passed through the sample, and the reference light beam, which has not passed through the sample.
Confocal scanning microscopes have the advantages in that, for example, three-dimensional image information can be obtained easily. If the confocal scanning microscopes can be constituted as interference microscopes, such confocal scanning types of interference microscopes will be very advantageous in the investigation of phase information of phase objects. However, heretofore, such a confocal scanning type of interference microscope has not been provided in practice. Specifically, when a light beam and a reference light beam are caused to scan, the lengths of their optical paths fluctuate easily. This is the reason why such a confocal scanning type of interference microscope has not been provided in practice.